This invention relates to gas turbine engines and particularly to a means for detecting surge.
As is well known, surge in an axial flow compressor gas turbine engine has been a problem perplexing the industry since its inception. While the phenomena of surge is not completely understood, suffice it to say that flow separation around the compressor blades manifests a pressure pulsation, which not only can be injurious to the engine but can result in engine failure. Also well known is the fact that the fuel control customarily comes equipped with a means for providing surge protection by scheduling a predetermined engine operation line or surge line and by monitoring and computing certain engine parameters, limits fuel flow to operate the engine below the surge line. Examples of fuel controls of the type described above are exemplified by the JFC-12, JFC-25, and JFC-60 manufactured by Hamilton Standard Division of United Technologies Corporation.
However, because the schedules are not always accurate, or owing to inaccurate sensors, or distorted signals and the like, certain engines require additional means to detect surge. For example, the U.S. Pat. No. 4,060,980 filed on Nov. 19, 1975 to F. L. Elsaesser, et al and assigned to the same assignee, and U.S. Pat. No. 3,426,322 granted to H. A. Balo on Feb. 4, 1969 disclose surge detection systems. It is important to recognize that the surge detection means described in this patent application and patent, as well as all other heretofore known surge detectors, not only require at least the measurement of two operating engine parameters, they also require instrumentation within the engine. This instrumentation normally requires access holes in the engine casings and probes protruding into the gas path.
We have found that we can obtain an efficacious surge detector by measuring engine inlet temperature rate of change or rise and generating a surge detected signal upon it reaching a predetermined value. The temperature probe can be located at the inlet of the engine, thus obviating the necessity of drilling holes into the engine case. In certain installations, as a means of protecting against false surge detection, the system may be designed to be coupled with another engine operating parameter, such as compressor rotor speed, compressor discharge pressure and the like.